Process to prepare a waxy raffinate

ABSTRACT

A process to prepare a waxy raffinate product by
     (a) hydrocracking/hydroisomerizing a Fischer-Tropsch derived feed, wherein weight ratio of compounds having at least 60 or more carbon atoms and compounds having at least 30 carbon atoms in the Fischer-Tropsch product is at least 0.2 and wherein at least 30 wt % of compounds in the Fischer-Tropsch derived feed have at least 30 carbon atoms; and,   (b) isolating from the product of step (a) a waxy raffinate product having a T10 wt % boiling point of between 200° C. and 450° C. and a T90 wt % boiling point of between 400° C. and 650° C.

FIELD OF THE INVENTION

The invention is directed to a process to prepare a waxy raffinate froma Fiseher-Tropsch product. The waxy raffinate product as obtained inthis process may find application as a feedstock to prepare alubricating base oil.

BACKGROUND OF THE INVENTION

Said preparation of the base oil and the preparation of the waxyraffinate product may take place at different locations. Suitably thewaxy raffinate product is prepared at the location where theFischer-Tropsch product is prepared and the lubricating base oil isprepared at a location near the main markets for these products.Generally these locations will be different resulting in that the waxyraffinate products will have to be transported, for example by ship, tothe lubricant base oil manufacturing location. This manner of preparingbase oils is advantageous because only-one product has to be shipped tothe potential base oil and lubricant markets instead of transporting thevarious base oils grades which may be prepared from the waxy raffinateproduct.

Prior art base oils as described in for example WO-A-0014179,WO-A-0014183, WO-A-0014187 and WO-A-0014188 comprise at least 95 wt % ofnon-cyclic isoparaffins. WO-A-0118156 describes a base oil derived froma Fischer-Tropsch product having 10%. Also the base oils as disclosed inapplicant's patent applications EP-A-776959 or EP-A-668342 have beenfound to comprise less than 10 wt % of cyclo-paraffins. Applicantsrepeated Example 2 and 3 of EP-A-776959 and base oils were obtained,from a waxy Fischer-Tropsch synthesis product, wherein the base oilsconsisted of respectively about 96 wt % and 93 wt % of iso- and normalparaffins. Applicants further prepared a base oil having a pour point of−21° C. by catalytic dewaxing a Shell MDS Waxy Raffinate (as obtainablefrom Shell MDS Malaysia Sdn Bhd) using a catalyst comprising syntheticferrierite and platinum according to the teaching of EP-A-668342 andfound that the content of iso- and normal paraffins was about 94 wt %.Thus these prior art base oils derived from a Fischer-Tropsch synthesisproduct had at least a cyclo-paraffin content of below 10 wt %.Furthermore the base oils as disclosed by the examples of applicationWO-A-9920720 will not comprise a high cyclo-paraffin content. Thisbecause feedstock and preparation used in said examples is very similarto the feedstock and preparation to prepare the above prior art samplesbased on EP-A-776959 and EP-A-668342.

SUMMARY OF THE INVENTION

Applicants have now found a method to prepare a waxy raffinate product,from which lubricating base oil composition can be prepared having ahigher cyclo-paraffin content and a resulting improved solvency whencompared to the disclosed base oils. This is found to be advantageous infor example industrial formulations such as turbine oils and hydraulicoils comprising for the greater part the base oil according to theinvention. Furthermore the base oil compositions will cause seals in forexample motor engines to swell more than the prior art base oils. Thisis advantageous because due to said swelling less lubricant loss will beobserved in certain applications. Applicants have found that such a baseoil is an excellent API Group III base oil having improved solvencyproperties.

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed to the following process. Process to prepare awaxy raffinate product by

-   (a) hydrocracking/hydroisomerisating a Fischer-Tropsch derived feed,    wherein weight ratio of compounds having at least 60 or more carbon    atoms and compounds having at least 30 carbon atoms in the    Fischer-Tropsch product is at least 0.2 and wherein at least 30 wt %    of compounds in the Fischer-Tropsch derived feed have at least 30    carbon atoms,-   (b) isolating from the product of step (a) a waxy raffinate product    having a T10 wt % boiling point of between 200 and 450° C. and a T90    wt % boiling point of between 400 and 650° C.

Applicants found that by performing thehydro-cracking/hydroisomerisation step with the relatively heavyfeedstock a way raffinate product is obtained from which valuableproducts may be prepared, such as the base oil product as described inthis application. A further advantage is that both fuels, for examplegas oil, and a waxy raffinate product suited for preparing base oils areprepared in one hydrocracking/hydroisomerisation process step.

The process of the present invention also results in middle distillateshaving exceptionally good cold flow properties. These excellent coldflow properties could perhaps be explained by the relatively high ratioiso/normal and especially the relatively high amount of di- and/ortrimethyl compounds. Nevertheless, the cetane number of the dieselfraction is more than excellent at values far exceeding 60, often valuesof 70 or more are obtained. In addition, the sulphur content isextremely low, always less than 50 ppmw, usually less than 5 ppmw and inmost case the sulphur content is zero. Further, the density ofespecially the diesel fraction is less than 800 kg/m³, in most cases adensity is observed between 765 and 790 kg/m³, usually around 780 kg/m³(the viscosity at 100° C. for such a sample being about 3.0 cSt).Aromatic compounds are virtually absent, i.e. less than 50 ppmw,resulting in very low particulate emissions. The polyaromatic content iseven much lower than the aromatic content, usually less than 1 ppmw.T95, in combination with the above properties, is below 380° C., oftenbelow 350° C.

The process as described above results in middle distillates havingextremely good cold flow properties. For instance, the cloud point ofany diesel fraction is usually below −18° C., often even lower than −24°C. The CFPP is usually below −20° C., often −28° C. or lower. The pourpoint is usually below −18° C., often below −24° C.

The relatively heavy Fischer-Tropsch derived feed as used in step (a)has at least 30 wt %, preferably at least 50 wt %, and more preferablyat least 55 wt % of compounds having at least 30 carbon atoms.Furthermore the weight ratio of compounds having at least 60 or morecarbon atoms and compounds having at least 30 carbon atoms of theFischer-Tropsch derived feed is at least 0.2, preferably at least 0.4and more preferably at least 0.55. The Fischer-Tropsch derived feed ispreferably derived from a Fischer-Tropsch product which comprises a C₂₀⁺ fraction having an ASF-alpha value (Anderson-Schulz-Flory chain growthfactor) of at least 0.925, preferably at least 0.935, more preferably atleast 0.945, even more preferably at least 0.955.

The initial boiling point of the Fischer-Tropsch derived feed may rangeup to 400° C., but is preferably below 200° C. Preferably at least anycompounds having 4 or less carbon atoms and any compounds having aboiling point in that range are separated from a Fischer-Tropschsynthesis product before the Fischer-Tropsch synthesis product is usedas a Fischer-Tropsch derived feed in step (a). The Fischer-Tropschderived feed as described in detail above will for the greater partcomprise of a Fischer-Tropsch synthesis product, which has not beensubjected to a hydroconversion step as defined according to the presentinvention. The content of non-branched compounds in the Fischer-Tropschsynthesis product will therefore be above 80 wt %. In addition to thisFischer-Tropsch product also other fractions may be part of theFischer-Tropsch derived feed. Possible other fractions may suitably beany high boiling fraction obtained in step (b) or any surplus waxyraffinate product, which cannot be shipped away to lubricatingmanufactures. By recycling this fraction additional middle distillatesmay be prepared.

Such a Fischer-Tropsch product can be obtained by any process whichyields a relatively heavy Fischer-Tropsch product. Not allFischer-Tropsch processes yield such a heavy product. An example of asuitable Fischer-Tropsch process is described in WO-A-9934917 and inAU-A-698392 both of which are hereby incorporated by reference. Theseprocesses may yield a Fischer-Tropsch product as described above.

The Fischer-Tropsch derived feed and the resulting waxy raffinateproduct will contain no or very little sulphur and nitrogen containingcompounds. This is typical for a product derived from a Fischer-Tropschreaction, which uses synthesis gas containing almost no impurities.Sulphur and nitrogen levels will generally be below the detectionlimits, which are currently 5 ppm for sulphur and 1 ppm for nitrogen.

The Fischer-Tropsch derived feed may optionally be subjected to a mildhydrotreatment step in order to remove any oxygenates and saturate anyolefinic compounds present in the reaction product of theFischer-Tropsch reaction. Such a hydrotreatment is described inEP-B-668342 hereby incorporated by reference. The mildness of thehydrotreating step is preferably expressed in that the degree ofconversion in this step is less than 20 wt % and more preferably lessthan 10 wt %. The conversion is here defined as the weight percentage ofthe feed boiling above 370° C., which reacts to a fraction boiling below370° C. After such a mild hydrotreatroent lower boiling compounds,having four or less carbon atoms and other compounds boiling in thatrange, will preferably be removed from the effluent before it is used instep (a).

The hydrocracking/hydroisomerisation reaction of step (a) is preferablyperformed in the presence of hydrogen and a catalyst, which catalyst canbe chosen from those known to one skilled in the art as being suitablefor this reaction. Catalysts for use in step (a) typically comprise anacidic functionality and a hydrogenation/dehydrogenation functionality.Preferred acidic functionality's are refractory metal oxide carriers.Suitable carrier materials include silica, alumina, silica-alumina,zirconia, titania and mixtures thereof. Preferred carrier materials forinclusion in the catalyst for use in the process of this invention aresilica, alumina and silica-alumina. A particularly preferred catalystcomprises platinum supported on a silica-alumina carrier. If desired,applying a halogen moiety, in particular fluorine, or a phosphorousmoiety to the carrier, may enhance the acidity of the catalyst carrier.Examples of suitable hydrocracking/hydroisomerisation processes andsuitable catalysts are described in WO-A-0014179, EP-A-532118,EP-A-666894 and the earlier referred to EP-A-776959 all are herebyincorporated by reference.

Preferred hydrogenation/dehydrogenation functionalities are Group VIIInon-noble metals, for example nickel and cobalt, optionally incombination with molybdenum or copper, and Group VIII noble metals, forexample palladium and more preferably platinum or platinum/palladiumalloys. The catalyst may comprise the noble metalhydrogenation/dehydrogenation active component in an amount of from0.005 to 5 parts by weight, preferably from 0.02 to 2 parts by weight,per 100 parts by weight of carrier material. A particularly preferredcatalyst for use in the hydroconversion stage comprises platinum in anamount in the range of from 0.05 to 2 parts by weight, more preferablyfrom 0.1 to 1 parts by weight, per 100 parts by weight of carriermaterial. The catalyst may also comprise a binder to enhance thestrength of the catalyst. The binder can be non-acidic. Examples areclays and other binders known to one skilled in the art.

In step (a) the feed is contacted with hydrogen in the presence of thecatalyst at elevated temperature and pressure. The temperaturestypically will be in the range of from 175 to 380° C., preferably higherthan 250° C. and more preferably from 300 to 370° C. The pressure willtypically be in the range of from 10 to 250 bar and preferably between20 and 80 bar. Hydrogen may be supplied at a gas hourly space velocityof from 100 to 10000 Nl/l/hr, preferably from 500 to 5000 Nl/l/hr. Thehydrocarbon feed may be provided at a weight hourly space velocity offrom 0.1 to 5 kg/l/hr, preferably higher than 0.5 kg/l/hr and morepreferably lower than 2 kg/l/hr. The ratio of hydrogen to hydrocarbonfeed may range from 100 to 5000 Nl/kg and is preferably from 250 to 2500Nl/kg.

The conversion in step (a) as defined as the weight percentage of thefeed boiling above 370° C. which reacts per pass to a fraction boilingbelow 370° C., is at least 20 wt %, preferably at least 25 wt %, butpreferably not more than 80 wt %, more preferably not more than 70 wt %.The feed as used above in the definition is the total hydrocarbon feedfed to step (a), thus also any optional recycle of the higher boilingfraction as obtained in step (b).

In step (b) the product of step (a) is separated into one or more gasoil fractions, a waxy raffinate product having a T10 wt % boiling pointof between 200 and 450° C. and a T90 wt % boiling point of between 400and 650° C. and more preferably a T90 wt % boiling point of below 550°C. Depending on the conversion in step (a) and the properties of thetotal feed to step (a) also a higher boiling fraction may be obtained instep (b).

The separation in step (b) is preferably performed by means of a firstdistillation at about atmospheric-conditions, preferably at a pressureof between 1.2-2 bara, wherein the gas oil product and lower boilingfractions, such as naphtha and kerosine fractions, are separated fromthe higher boiling fraction of the product of step (a). The higherboiling fraction, of which suitably at least 95 wt % boils above 370°C., is subsequently further separated in a vacuum distillation stepwherein a vacuum gas oil fraction, the waxy raffinate product and thehigher boiling fraction are obtained. The vacuum distillation issuitably performed at a pressure of between 0.001 and 0.05 bara.

The vacuum distillation of step (b) is preferably operated such that thedesired waxy raffinate product is obtained boiling in the specifiedrange and having a kinematic viscosity at 100° C. of preferably between3 and 10 cSt.

The waxy raffinate product as obtained by the above process hasproperties, such as pour point and viscosity, which makes it suitable tobe transported, suitable by ships, to a lubricating base oilmanufacturing location. Preferably the waxy raffinate is stored andtransported in the absence of oxygen such to avoid oxidation of theparaffin molecules present in the waxy raffinate product. Suitablenitrogen blanketing is applied during said storage and transport.Preferably the waxy raffinate product has a pour point of above 0° C.This makes it possible to transport the waxy raffinate as a solid by forexample keeping the product at ambient temperatures. Transporting theproduct in the solid state is advantageous because it further limits theingress of oxygen and thus avoids oxidation. Means to liquefy theproduct at the unloading facility should be present. Preferably indirectheating means such as steam heated coils are present in the storagetanks, such that the product may be liquefied before being dischargedfrom the tanks. Transport lines are also preferably provided with meansto keep the product in a liquid state.

The waxy raffinate product may find various applications. A most suitedapplication is to use the waxy raffinate product as feedstock to preparelubricating base oils by subjecting the waxy raffinate product to a pourpoint reducing step. Optionally the waxy raffinate product may beblended with slack wax in order to upgrade the slack wax properties withrespect to sulphur, nitrogen and saturates content before subjecting thewaxy raffinate to a pour point reducing step.

With a pour point reducing treatment is understood every process whereinthe pour point of the base oil is reduced by more than 10° C.,preferably more than 20° C., more preferably more than 25° C.

The pour point reducing treatment can be performed by means of aso-called solvent dewaxing process or by means of a catalytic dewaxingprocess. Solvent dewaxing is well known to those skilled in the art andinvolves admixture of one or more solvents and/or wax precipitatingagents with the waxy raffinate product and cooling the mixture to atemperature in the range of from −10° C. to −40° C., preferably in therange of from −20° C. to −35° C., to separate the wax from the oil. Theoil containing the wax is usually filtered through a filter cloth whichcan be made of textile fibres, such as cotton; porous metal cloth; orcloth made of synthetic materials. Examples of solvents which may beemployed in the solvent dewaxing process are C₃-C₆ ketones (e.g. methylethyl ketone, methyl isobutyl ketone and mixtures thereof), C₆-C₁₀aromatic hydrocarbons (e.g. toluene), mixtures of ketones and aromatics(e.g. methyl ethyl ketone and toluene), autorefrigerative solvents suchas liquefied, normally gaseous C₂-C₄ hydrocarbons such as propane,propylene, butane, butylene and mixtures thereof. Mixtures of methylethyl ketone and toluene or methyl ethyl ketone and methyl isobutylketone are generally preferred. Examples of these and other suitablesolvent dewaxing processes are described in Lubricant Base Oil and WaxProcessing, Avilino Sequeira, Jr, Marcel Dekker Inc., New York, 1994,Chapter 7.

A preferred pour point reducing process is the catalytic dewaxingprocess. With such a process it has been found that base oils having apour point of even below −40° C. can be prepared when starting from thewaxy raffinate product according to the present process.

The catalytic dewaxing process can be performed by any process whereinin the presence of a catalyst and hydrogen the pour point of the baseoil precursor fraction is reduced as specified above. Suitable dewaxingcatalysts are heterogeneous catalysts comprising a molecular sieve andoptionally in combination with a metal having a hydrogenation function,such as the Group VIII metals. Molecular sieves, and more suitablyintermediate pore size zeolites, have shown a good catalytic ability toreduce the pour point of a base oil precursor fraction under catalyticdewaxing conditions. Preferably the intermediate pore size zeolites havea pore diameter of between 0.35 and 0.8 nm. Suitable intermediate poresize zeolites are ZSM-5, ZSM-12, ZSM-22, ZSM-23, SSZ-32, ZSM-35 andZSM-48. Another preferred group of molecular sieves are thesilica-aluminaphosphate (SAPO) materials of which SAPO-11 is mostpreferred as for example described in U.S. Pat. No. 4,859,311 herebyincorporated by reference. ZSM-5 may optionally be used in its HZSM-5form in the absence of any Group VIII metal. The other molecular sievesare preferably used in combination with an added Group VIII metal.Suitable Group VIII metals are nickel, cobalt, platinum and palladium.Examples of possible combinations are Ni/ZSM-5, PtIZSM-23, Pd/ZSM-23,Pt/ZSM-48 and Pt/SAPO-11. Further details and examples of suitablemolecular sieves and dewaxing conditions are for example described inWO-A-9718278, U.S. Pat. No. 5,053,373, U.S. Pat. No. 5,252,527 and U.S.Pat. No. 4,574,043 all are hereby incorporated by reference.

The dewaxing catalyst suitably also comprises a binder. The binder canbe a synthetic or naturally occurring (inorganic) substance, for exampleclay, silica and/or metal oxides. Natural occurring clays are forexample of the montmorillonite and kaolin families. The binder ispreferably a porous binder material, for example a refractory oxide ofwhich examples are: alumina, silica-alumina, silica-magnesia,silica-zirconia, silica-thoria, silica-beryllia, silica-titania as wellas ternary compositions for example silica-alumina-thoria,silica-alumina-zirconia, silica-alumina-magnesia andsilica-magnesia-zirconia. More preferably a low acidity refractory oxidebinder material, which is essentially free of alumina, is used. Examplesof these binder materials are silica, zirconia, titanium dioxide,germanium dioxide, boria and mixtures of two or more of these of whichexamples are listed above. The most preferred binder is silica.

A preferred class of dewaxing catalysts comprises intermediate zeolitecrystallites as described above and a low acidity refractory oxidebinder material which is essentially free of alumina as described above,wherein the surface of the aluminosilicate zeolite crystallites has beenmodified by subjecting the aluminosilicate zeolite crystallites to asurface dealumination treatment. A preferred dealumination treatmentcomprises contacting an extrudate of the binder and the zeolite with anaqueous solution of a fluorosilicate salt as described in for exampleU.S. Pat. No. 5,157,191 or WO-A-0029511 both of which are herebyincorporated by reference. Examples of suitable dewaxing catalysts asdescribed above are silica bound and dealuminated PtIZSM-5, silica boundand dealuminated PtIZSM-23, silica bound and dealuminated Pt/ZSM-12,silica bound and dealuminated Pt/ZSM-22, as for example described inWO-A-0029511 and EP-B-832171 hereby incorporated by reference.

Catalytic dewaxing conditions are known in the art and typically involveoperating temperatures in the range of from 200 to 500° C., suitablyfrom 250 to 400° C., hydrogen pressures in the range of from 10 to 200bar, preferably from 40 to 70 bar, weight hourly space velocities (WHSV)in the range of from 0.1 to 10 kg of oil per litre of catalyst per hour(kg/l/hr), suitably from 0.2 to 5 kg/l/hr, more suitably from 0.5 to 3kg/l/hr and hydrogen to oil ratios in the range of from 100 to 2,000litres of hydrogen per litre of oil. By varying the temperature between275, suitably between 315 and 375° C. at between 40-70 bars, in thecatalytic dewaxing step it is possible to prepare base oils havingdifferent pour point specifications varying from suitably −10 to −60° C.

The effluent or separate boiling fractions of the catalytic or solventdewaxing step are optionally subjected to an additional hydrogenationstep, also referred to as a hydrofinishing step for example if theeffluent contains olefins or when the product is sensitive tooxygenation or when colour needs to be improved. This step is suitablycarried out at a temperature between 180 and 380° C., a total pressureof between 10 to 250 bar and preferably above 100 bar and morepreferably between 120 and 250 bar. The WHSV (Weight hourly spacevelocity) ranges from 0.3 to 2 kg of oil per litre of catalyst per hour(kg/l.h).

The hydrogenation catalyst is suitably a supported catalyst comprising adispersed Group VIII metal. Possible Group VIII metals are cobalt,nickel, palladium and platinum. Cobalt and nickel containing catalystsmay also comprise a Group VIB metal, suitably molybdenum and tungsten.Suitable carrier or support materials are low acidity amorphousrefractory oxides. Examples of suitable amorphous refractory oxidesinclude inorganic oxides, such as alumina, silica, titania, zirconia,boria, silica-alumina, fluorided alumina, fluorided silica-alumina andmixtures of two or more of these.

Examples of suitable hydrogenation catalysts are nickel-molybdenumcontaining catalyst such as KF-847 and KF-8010 (AKZO Nobel) M-8-24 andM-8-25 (BASF), and C-424, DN-190, HDS-3 and HDS-4 (Criterion);nickel-tungsten containing catalysts such as NI-4342 and NI-4352(Engelhard) and C-454 (Criterion); cobalt-molybdenum containingcatalysts such as KF-330 (AKZO-Nobel), HDS-22 (Criterion) and HPC-601(Engelhard). Preferably platinum containing and more preferably platinumand palladium containing catalysts are used. Preferred supports forthese palladium and/or platinum containing catalysts are amorphoussilica-alumina. Examples of suitable silica-alumina carriers aredisclosed in WO-A-9410263 hereby incorporated by reference. A preferredcatalyst comprises an alloy of palladium and platinum preferablysupported on an amorphous silica-alumina carrier of which thecommercially available catalyst C-624 of Criterion Catalyst Company(Houston, Tex.) is an example.

The dewaxed product is suitable separated into one or more base oilproducts having different viscosities by means of distillation,optionally in combination with an initial flashing step. The separationinto the various fractions may suitably be performed in a vacuumdistillation column provided with side stripers to separate the fractionfrom said column. In this mode it is found possible to obtain forexample a base oil having a viscosity between 2-3 cSt, a base oil havinga viscosity between 4-6 cSt and a base oil having a viscosity between7-10 cSt product simultaneously from a single waxy raffinate product(viscosities as kinematic viscosity at 100° C.). By straightforwardoptimising the product slate and minimising the amount of non-base oilintermediate fractions it has been found possible to prepare base oilsin a sufficiently high yield having a good Noack volatility properties.For example, base oils having a kinematic viscosity at 100° C. ofbetween 3.5 and 6 cSt have been obtained which have a Noack volatilityof between 6 and 14 wt %.

It has been found that a lubricating base oil can be prepared startingfrom this waxy raffinate product which base oil comprises preferably atleast 98 wt % saturates, more preferably at least 99.5 wt % saturatesand most preferably at least 99.9 wt %. This saturates fraction in thebase oil comprises between 10 and 40 wt % of cyclo-paraffins. Preferablythe content of cyclo-paraffins is less than 30 wt % and more preferablyless than 20 wt %. Preferably the content of cyclo-paraffins is at least12 wt %. The unique and novel base oils are further characterized inthat the weight ratio of 1-ring cyclo-paraffins relative tocyclo-paraffins having two or more rings is greater than 3 preferablygreater than 5. It was found that this ratio is suitably smaller than15.

The cyclo-paraffin content as described above is measured by thefollowing method. Any other method resulting in the same results mayalso be used. The base oil sample is first separated into a polar(aromatic) phase and a non-polar (saturates) phase by making use of ahigh performance liquid chromatography (HPLC) method IP368/01, whereinas mobile phase pentane is used instead of hexane as the method states.The saturates and aromatic fractions are then analyzed using a FinniganMAT90 mass spectrometer equipped with a Field desorption/FieldIonisation (FD/FI) interface, wherein FI (a “soft” ionisation technique)is used for the semi-quantitative determination of hydrocarbon types interms of carbon number and hydrogen deficiency. The type classificationof compounds in mass spectrometry is determined by the characteristicions formed and is normally classified by “z number”. This is given bythe general formula for all hydrocarbon species: C_(n)H_(2n+z). Becausethe saturates phase is analysed separately from the aromatic phase it ispossible to determine the content of the different (cyclo)-paraffinshaving the same stoichiometry. The results of the mass spectrometer areprocessed using commercial software (poly 32; available from SierraAnalytics LLC, 3453 Dragoo Park Drive, Modesto, Calif. GA95350 USA) todetermine the relative proportions of each hydrocarbon type and theaverage molecular weight and polydispersity of the saturates andaromatics fractions.

The base oil composition preferably has a content of aromatichydrocarbon compounds of less than 1 wt %, more preferably less than 0.5wt % and most preferably less than 0.1 wt %, a sulphur content of lessthan 20 ppm and a nitrogen content of less than 20 ppm. The pour pointof the base oil is preferably less than −30° C. and more preferablylower than −40° C. The viscosity index is higher than 120. It has beenfound that the novel base oils typically have a viscosity index of below140.

The base oils itself may find application as part of for example anAutomatic Transmission Fluids (ATF), automotive (gasoline or diesel)engine oils, turbine oils, hydraulic oils, electrical oils ortransformer oils and refrigerator oils.

The invention will be illustrated with the following non-limitingexamples.

EXAMPLE 1

A waxy raffinate product was obtained by feeding continuously a C₅-C₇₅₀°C.⁺ fraction of the Fischer-Tropsch product, as obtained in Example VIIusing the catalyst of Example III of WO-A-9934917 to a hydrocrackingstep (step (a)). The feed contained about 60 wt % C₃₀+ product. Theratio C₆₀+/C₃₀+ was about 0.55. In the hydrocracking step the fractionwas contacted with a hydrocracking catalyst of Example 1 of EP-A-532118.

The effluent of step (a) was continuously distilled to give lights,fuels and a residue “R” boiling from 370° C. and above. The yield of gasoil fraction on fresh feed to hydrocracking step was 43 wt %. The mainpart of the residue “R” was recycled to step (a) and a remaining partwas separated by means of a vacuum distillation into a waxy raffinateproduct having the properties as in Table 1 and a fraction boiling above510° C.

The conditions in the hydrocracking step (a) were: a fresh feed WeightHourly Space Velocity (WHSV) of 0.8 kg/l.h, recycle feed WHSV of 0.2kg/l.h, hydrogen gas rate=1000 Nl/kg, total pressure=40 bar, and areactor temperature of 335° C.

TABLE 1 Density at 70° C. (kg/m³) 779.2 vK@100 (cSt) 3.818 pour point (°C.) +18 Boiling point data as  5% 355° C. temperature at which a 10%370° C. wt % is recovered. 50% 419° C. 90% 492° C. 95% 504° C.

EXAMPLE 2

The waxy raffinate product of Example 1 was dewaxed to prepare a baseoil by contacting the product with a dealuminated silica bound ZSM-5catalyst comprising 0.7% by weight Pt and 30 wt % ZSM-5 as described inExample 9 of WO-A-0029511. The dewaxing conditions were 40 bar hydrogen,WHSV=1 kg/l.h and a temperature of 340° C.

The dewaxed oil was distilled into three base oil fractions: boilingbetween 378 and 424° C. (yield based on feed to dewaxing step was 14.2wt %), between 418-455° C. (yield based on feed to dewaxing step was16.3 wt %) and a fraction boiling above 455° C. (yield based on feed todewaxing step was 21.6 wt %). See Table 2 for more details.

TABLE 2 Light Medium Heavy Grade Grade Grade density at 20° C. 805.8814.6 822.4 pour point (° C.) <−63 <−51 −45 kinematic viscosity at 19.0635.0 40° C. (cSt) kinematic viscosity at 100° C. (cSt) 3.16 4.144 6.347VI n.a. 121 134 Noack volatility (wt %) n.a. 10.8 2.24 sulphur content(ppm) <1 ppm <1 ppm <5 ppm saturates (% w) n.a. 99.9 n.a. Content ofcyclo- n.a. 18.5 n.a. paraffins (wt %) (*) Dynamic viscosity as measuredby CCS at n.a. 3900 cP n.a. −40° C. (*) as determined by means of aFinnigan MAT90 mass spectrometer equipped with a Field desorption/fieldionisation interface on the saturates fraction of said base oil. n.a.:not applicable n.d.: not determined

EXAMPLE 3

Example 2 was repeated except that the dewaxed oil was distilled intothe different three base oil products of which the properties arepresented in Table 3.

TABLE 3 Light Medium Heavy Grade Grade Grade density at 20° C. 809.1817.2 825.1 pour point (° C.) <−63 <−51 −39 kinematic viscosity at 23.3243.01 40° C. (cSt) kinematic viscosity at 3.181 4.778 7.349 100° C.(cSt) VI n.a. 128 135 Noack volatility (wt %) n.a. 7.7 n.a. sulphurcontent (ppm) <5 ppm <5 ppm <5 ppm saturates (% w) 99.0 Dynamicviscosity as measured by CCS at 5500 cP −40° C. Yield based on feed tocat dewaxing step 15.3 27.4 8.9 (wt %)

EXAMPLE 4

Example 2 was repeated except that the that the dewaxed oil wasdistilled into the different three base oil products and oneintermediate raffinate (I.R.) of which the properties are presented inTable 4.

TABLE 4 Light Medium Heavy Grade I.R. Grade Grade density at 20° C. 806811.3 817.5 824.5 pour point (° C.) <−63 −57 <−51 −39 Kinematicviscosity at 10.4 23.51 42.23 40° C. (cSt) Kinematic viscosity at 100°C. (cSt) 2.746 3.501 4.79 7.24 VI 103 127 135 Noack volatility n.a. 6.81.14 sulphur content (ppm) <5 ppm <5 ppm <5 ppm Saturates (% w) n.d.99.5 Dynamic viscosity as 5500 cP measured by CCS at −40° C. Yield basedon CDW feed 22.6 8.9 22.6 11.1 n.a.: not applicable n.d.: not determinedExamples 2-4 illustrate that from the waxy raffinate product as obtainedby the process of the present invention base oils are prepared in a highyield and wherein the base oils have excellent viscometric properties.

1. A process to prepare a waxy raffinate product comprising (a)hydrocracking/hydroisomerizing a Fischer-Tropsch derived feed, toproduce a Fischer-Tropsch product wherein weight ratio of compoundshaving at least 60 or more carbon atoms and compounds having at least 30carbon atoms in the Fischer-Tropsch product is at least 0.4 and whereinat least 30 wt % of compounds in the Fischer-Tropsch derived feed haveat least 30 carbon atoms; and, (b) isolating from the product of step(a) a waxy raffinate product having a T10 wt % boiling point of between200° C. and 450° C. and a T90 wt % boiling point of between 400° C. and650° C.
 2. The process of claim 1, wherein at least 50 wt % of compoundsin the Fischer-Tropsch derived feed have at least 30 carbon atoms. 3.The process of claims 1, wherein the Fischer-Tropsch derived feed isderived from a Fischer-Tropsch product comprising a C₂₀ ⁺ fractionhaving an ASF-alpha value (Anderson-Schulz-Flory chain growth factor) ofat least 0.925.
 4. The process of claims 1, wherein the conversion instep (a) is between 25 wt % and 70 wt %.
 5. The process of claims 1,wherein the T90 wt % boiling point of the waxy raffinate product isbelow 550° C.
 6. The process of claims 1, wherein the waxy raffinateproduct has a kinematic viscosity at 100° C. of between 3 cSt and 10cSt.
 7. A process for preparing lubricating base oils comprising: (a)preparing a waxy raffinate product by the process comprising (i)hydrocracking/hydroisomerizing a Fischer-Tropsch derived feed, toproduce a Fischer-Tropsch product wherein weight ratio of compoundshaving at least 60 or more carbon atoms and compounds having at least 30carbon atoms in the Fischer-Tropsch product is at least 0.4 and whereinat least 30 wt % of compounds in the Fischer-Tropsch derived feed haveat least 30 carbon atoms; and, (ii) isolating from the product of step(a) a waxy raffinate product having a T10 wt % boiling point of between200° C. and 450° C. and a T90 wt % boiling point of between 400° C. and650° C. (b) subjecting the waxy raffinate from step (a) to a pour pointreducing step to produce a dewaxed product.
 8. The process of claim 7,wherein the pour point reducing step comprises catalystic dewaxing. 9.The process of claim 7, further comprising: (b) distilling the dewaxedproduct into one or more fractions.
 10. The process of claim 9, whereinone of the fractions from step (c) comprises at least 98 wt % saturates.11. The process of claim 10, wherein the fraction comprising at least 98wt % saturated comprises between 12 wt % and 20 wt % cyclo-paraffins.12. The process of claim 7, further comprising transporting the waxyraffinate product to a location for pour point reduction wherein thewaxy raffinate has a pour point of 0° C. and is under nitrogenblanketing during transportation.